When handling products consisting of a mixture of pieces of material or fragments of different materials there exists a need to subdivide the mixture into a number of fractions, each containing only certain definite types of materials. Examples of mixtures which require subdividing are fresh-cut peat (mixed with soil, stones, sticks and twigs) and refuse (usually household refuse). There are of course many other mixtures where a corresponding need exists.
According to an applied alternative for handling refuse, the refuse is first ground down in mills and then sorted into a number of fractions in mechanical separation plants. In a similar manner, peat is separated from irrelevant materials (soil, stones, sticks and twigs).
For reliable operation of the plants it is necessary for the mixture to be supplied to them in a uniformly thick layer of a certain maximum thickness and of a relatively large width.
In addition, the thickness of the layer and its flow rate must be relatively independent of time. Achieving a layer with the above-mentioned properties has so far been fraught with problems.
The reason for the difficulties mentioned is that mixtures of the type mentioned above consist of articles of different density, different elasticity, irregular shape, a certain degree of adhesion, and of varying moisture content. When carrying refuse, for example, on conveyors or in conveying troughs it has a tendency to form a stringy substance which has an adverse effect on the separation plant used. Further, it is not economically feasible to design the transport devices so that the refuse, when conveyed by them, is already in the thin layers required by the subsequent separation plant. There is consequently a need for equipment which spreads the stringy substance on the transport devices in a wide and uniformly thick layer which is supplied to the separation plant along its entire width.
Another problem associated with equipment used at present is that the flow rate of the mixtures varies. In the case of refuse, for example, this is due to uneven discharge from the mill. Such variations in the flow reduce the capacity of the subsequent separation plant. There is accordingly also a need for devices which equalize such variations.
For optimum operation of the separation plant it is, as a rule, necessary for the distribution of the different types of materials to be largely the same for all of the mixture supplied to the plant.
A solution which partially solves the problem of achieving a uniformly thick layer of material is known. This solution consists of vibrating troughs fitted with a number of relatively low plough-like protrusions situated one after the other with their points facing the direction of transporation. Through the agency of the protrusions the material is spread out towards the sides of the vibrating trough. A serious disadvantage of this solution is that the protrusions act as obstructions, whereby the transport capacity of the vibrating trough is reduced at the same time as an undesirable division of the material occurs.